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I 4.19 Inheritance of the cameo phenotype in Indian blue peafowl is inherited as a Z-linked recessive trait. (a) Blue female crossed with cameo male. (b) Reciprocal cross of cameo female crossed with homozygous blue male.

which produces brown feathers, results from a Z-linked allele (Zca) that is recessive to the wild-type blue allele (ZCa+). If a blue-colored female (ZCa+W) is crossed with a cameo male (ZcaZca), all the F1 females are cameo (ZcaW) and all the Fj males are blue (ZCa+Zca) ( FIGURE 4.19). When the Fj are interbred, 1/4 of the F2 are blue males (ZCa+Zca), 1/4 are blue females (ZCa+W), % are cameo males (ZcaZca), and % are cameo females (ZcaW). The reciprocal cross of a cameo female with a homozygous blue male produces an Fj generation in which all offspring are blue and an Fj consisting of 72 blue males (ZCa+Zca and ZCa+ZCa+), 74 blue females (ZCa+ W), and 74 cameo females (Zca W).

In organisms with ZZ-ZW sex determination, the female always inherits her W chromosome from her mother, and she inherits her Z chromosome, along with any Z-linked alleles, from her father. In this system, the male inherits Z chromosomes, along with any Z-linked alleles, from both the mother and the father. This pattern of inheritance is the reverse of X-linked alleles in organisms with XX-XY sex determination.

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